The invention relates to an artificial foot.
An embodiment of an artificial foot is described in DE-PS 36 44 613. It relates to a non-articulated foot with a connecting component resting on the upper side of the core, which can be removed in the usual way and is connected by means of a threaded bolt inserted from the bottom of the foot into a drill hole in the core of the foot and screwed into a threaded nut in the connecting component. The front of the heel wedge locks approximately with the front of the core, with the heel wedge rising backwards to over half the height of the foot. The inner foot rests solely on the front of the core and the front of the heel wedge. The outer foot wraps the inner foot, as well as the bottom and back of the heel wedge and forms a thin layer of skin in the drill hole mentioned. In this artificial foot known from the prior art, the characteristics of the gait in the second phase of the rolling movement (when the heel is lifted) are determined almost exclusively by the flexible characteristics of the inner foot. The outer foot serves solely to protect against the penetration of water and aggressive agents, as well as to provide a cosmetic appearance for the surface of the foot.
In an artificial foot in accordance with DE-PS 36 44 613, which describes a generic concept, exceeding the maximum size and/or providing less than the minimal stiffness of the heel wedge leads to the desired soft tread of the front of the foot, although with a relatively small burden on the heel. However, in contrast to its neutral status in standing, in this situation the prosthetic foot takes on a position which falls backward so much that the amputee has the feeling that he has stepped in a hole and that getting out of it requires so much energy that he will have trouble expending it for an extended period. In contrast, the foot in accordance with the present invention reacts to pressure on the heel by decreasing the angle between the lower leg and the heel, called a plantar flexion, until the front of the foot is set down, at which point the prosthetic foot assumes a position which corresponds exactly to its neutral status while standing. Therefore, in contrast to a non-articulated foot with a large and soft heel wedge, it is possible with the present invention to roll forward with the front foot without expending much energy.
In a conventional joint construction, the joint axis in the foot is located very high, often at the level of the foot connecting surface, and has only a short lever arm from the vertically-acting plantar buffer. Since, in the design in accordance with the present invention, the pivot of the joint in the foot is situated very low (preferably in the lower quarter of the height of the foot), a lever arm considerably longer than the horizontally operating plantar buffer is located in the area of the foot connecting surface, so that with the same plantar moment, the force of the plantar buffer can be smaller when constructed in accordance with the invention. The plantar buffer in accordance with the invention can therefore be designed to be weaker, which also has a positive effect on its dimensions. Because of the low positioning of the joint, there is also a cosmetic advantage: the split in the joint found in many conventional solutions behind the joint axis in neutral position and in front of the joint axis in plantar flexion disappears completely in the design in accordance with the invention.
When the prosthesis wearer is in a standing position (state of standing upright) and viewed from the side (sagittal view), the vertical line from his center of gravity lies in front of the turning point of the joint in the foot and thus produces a knee-safeguarding moment via the elastic front of the foot, to the extent that the other components of the prosthesis are also arranged in relation to each other in accordance with the rules of prosthesis construction.
The foot in accordance with the invention avoids a sharp sinking in the heel area, with the related loss of center of gravity height, that is characteristic of the non-articulated foot of the prior art. The foot in accordance with the invention assumes a horizontal position after the front of the foot is set down, while the non-articulated foot ends up in a position which falls sharply backward. Other advantages of the foot in accordance with the invention lie in the maintenance-free and extremely durable design of the joint. No further assembly or adjustment to the foot is required. For that reason, in accordance with the invention it is possible to construct the outer foot to be completely sealed at the bottom of the foot as well.
Other characteristics of the invention are discussed in greater detail in combination with further advantages of the invention on the basis of explanatory examples.